The invention relates to a composition for producing magnetic or magnetizable moldings, comprising a powder made of a magnetic or magnetizable material, a mixture made of at least one epoxy-novolak resin, and also of at least one hardener, and comprising, if appropriate, at least one additive.
The invention further relates to a process for producing the composition and to a process for producing a molding made of the composition. Magnetic or magnetizable moldings are used by way of example as coil cores or coil formers. Coils with corresponding coil cores or coil formers are used by way of example as electromagnets, in generators, in laptop computers, in netbooks, in mobile telephones, in electric motors, in AC inverters, in electronic components for the automobile industry, in toys and in the electronics industry. The current method aimed at allowing production of moldings of any shape compresses a mixture made of a magnetic or magnetizable material, such as carbonyl iron powder, and also of a curable resin, into a mold, and then hardens the mixture. The resin used comprises, for example, an epoxy resin. This type of composition, where a composition made of carbonyl iron powder, of epoxy resin, and of a lubricant is molded to give a coil former, is known by way of example from U.S. Pat. No. 6,198,375. The epoxy resin/hardener mixture used here comprises Corvel Black® No. 10-7086 from Morton International. The lubricant used is a zinc stearate.
US-A 2008/0118766 discloses a mixture where an epoxy-novolak resin is used in conjunction with an amine hardener or with an acid hardener. The amount of the resin used here is from 0.05 to 1% by weight, based on the total weight of the mixture. A disadvantage of the composition known from the prior art is that dry premixing causes inhomogeneous distribution of the resin within the molding, and also causes long hardening times. Another disadvantage, particularly when epoxy resins are used, is that the storage stability of the finished mixture is only low, and the mixture is sensitive to moisture, particularly when anhydrides are used as hardeners.